1.Field
The present invention relates to a sensor device for spectrally resolved capture of optical detection radiation which emanates from a value document transported through a capture area of the sensor device in a predefined transport direction, and to a method for capturing a motion and/or a position of the value document relative to the capture area of the sensor device.
2.Related Art
Value documents are understood within the framework of the invention to be sheet-shaped objects that represent for example a monetary value or an authorization and hence should not be producible arbitrarily by unauthorized persons. Hence, they have features that are not easily produced, in particular copied, whose presence is an indication of authenticity, i.e. production by an authorized body. Important examples of such value documents are coupons, vouchers, checks and in particular bank notes.
Value documents, due to their value, involve a considerable incentive for forgery, i.e. for unauthorized production of documents with similar physical properties. To make such forgeries more difficult, value documents normally contain dyes and/or luminescent substances that are difficult to obtain and/or little known and have a characteristic remission spectrum or luminescence spectrum. For checking a value document for authenticity or the presence of a forgery, it is possible to capture optical radiation emanating from the value document in the by the characteristic part of the spectrum of the dye or luminescent substance by means of a sensor device and compare it to predefined spectra.
Such a check of the value documents can be effected in particular by machine, whereby the value documents are transported through a capture area of the sensor device. The capture area is defined here and hereinafter by the fact that radiation coming from said area is captured and detected or measured by the sensor device. Upon the machine check it is necessary to drive the employed sensor device such that it captures the properties of the value document when the latter is located in the capture area.
Upon such a machine check, the problem arises that the detection properties of the sensor device can change in the course of time or upon longer operation. In particular, there can occur for example a shift of spectra to higher or lower wavelengths, i.e. a spectral line in the spectrum of a predefined substance can be detected at a wave-length that is shifted relative to the actual wavelength corresponding to the spectral line. This behavior can impair the differentiation of authentic and forged value documents. This disadvantage is aggravated by a corresponding shift not being recognized, or not early enough.
The present invention is hence based on the object of providing a sensor device for spectrally resolved capture of optical detection radiation which emanates from a value document transported through a capture area of the sensor device in a predefined transport direction, wherein a change of detection properties of the sensor device can be easily recognized and, preferably, such changes can be simply compensated at least partly. Further, a corresponding method is to be stated.